Hydrofluoroolefins (HFOs), as compared with chlorofluorocarbons (CFCs), Hydrochlorofluorocarbons (HCFCs) and hydrofluorohydrocarbons (HFCs), do not contain chlorine, do not pose a threat to the Earth's ozone layer, and present a low global warming potential, and they have now become the research focus in F-chemical industries. Tetrafluoropropene, such as 1,3,3,3-tetrafluoropropene (HFO-1234ze) and 2,3,3,3-tetrafluoropropene (HFO-1234yf), have an ozone depletion potential value of 0 and a global warming potential value less than 10, and they are widely used in the fields such as chemical industry, fire fighting, aerospace, aviation and the like, and can be used as refrigerants, foaming agents, fire extinguishing agents, heat transfer media, propellants, gaseous dielectrics, bactericidal agent carriers, polymer monomers and intermediates of medicine and pesticide.
US20110190554 discloses a method for the synthesis of HFO-1234yf from 1,1,2,3,3,3-hexafluoropropene (HFP) as a starting material via a four-step reaction including hydrogenation, dehydrofluorination, hydrogenation and dehydrofluorination. However, some drawbacks are present in the method including difficult accessibility, high cost of reaction materials, and the need of introducing at least the stoichiometric amount of hydrogen. Actually, a higher molar ratio is often used in order to effectively control the exothermicity of the reaction in the hydrogenation step. In addition, introduction of excessive hydrogen at a higher temperature will also increase relevant safety risks, and the conditions are harsh, which is not favorable to industrial production.
WO2012099776 discloses a method for preparing HFO-1234yf from 1,1,2,3-tetrachloropropene (TCP) via 2-chloro-3,3,3-trifluoropropene (HCFC-1233xf) and 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb) by integrated three steps. However, in this method, firstly, chromium-based catalysts such as Cr2O3 and Cr2O3 supported on alumina or fluorinated alumina are involved. In fact, chromium-based catalysts are often used in industrial production of HFCs. These chromium-containing compounds and catalysts will cause damage to digestive tract and kidney of human, especially high-valence chromium has strong carcinogenic effect, is not friendly and will cause serious harm to people and the environment. Secondly, the intermediates HCFC-1233xf and HCFC-244bb are involved. These two halogenated hydrocarbons have approximate boiling points and azeotrope-like properties, and both of them are also easy to form an azeotrope with HF. Hence, a problem of difficult separation occurs, and the mixtures of them cannot be separated effectively by standard process and conventional methods, especially when they form a binary azeotrope or azeotrope-like component. Additionally, it has been found that during the preparation of HFO-1234yf from HCFC-244bb by dehydrochlorination, the HCFO-1233xf and HF impurities contained therein can seriously affect the life and product selectivity of the dehydrochlorination catalyst, and easily lead to a decrease in HFO-1234yf selectivity and in activity of the catalyst and loss of the catalyst life.
At present, four methods have mainly reported for preparation of HFO-1234ze including fluorine-chlorine exchange, dehydrohalogenation, telomerization and carbene reaction . With respect to fluorine-chlorine exchange, the method of synthesizing HFO-1234ze using 1-chloro-3,3,3-trifluoropropene (HCFC-1233zd) as material by one-step gas phase fluorination was reported in JP10007604, U.S. Pat. No. 6,472,573 and EP486333. However, the method has the disadvantage that the reaction material HCFC-1233zd is expensive, difficult to obtain, and inconvenient for transport. With respect to dehydrohalogenation, the method for synthesizing HFO-1234ze from 1,1,1,3,3-pentafluoropropane (HFC-245fa) as starting material was reported in U.S. Pat. No. 7,592,494, EP2014637, EP0974571, CN101265155, CN101466656 and JP10007605 respectively, but the reaction material HFC-245fa in the method is expensive. With respect to telomerization , US20050245773 and US20050245774 reported the preparation of HFO-1234ze using halogenated methane and halogenated ethylene as raw materials by telomerization followed by continuous fluorination. However, such synthesis method involves complicated route, the catalyst is expensive and prone to coking and deactivation, both the raw material conversion and the selectivity of target product are low. For preparation by carbene reaction, it has been reported in US20050245774 that HFO-1234ze can be obtained by reacting the difluorocarbene and vinylidene fluoride monomer in the same reactor at a high temperature above the cracking temperature of the difluorocarbene precursor. However, this synthesis method has no industrial application value with excessively high reaction temperature, low yield and harsh reaction conditions.
Although a number of methods have been currently disclosed for the preparation of HFO-1234ze and HFO-1234yf , they have shortcomings such as expensive and difficultly-accessible reaction materials, harsh reaction conditions, unfriendliness of the catalyst to environments, and difficult separation of reaction intermediates. Thus, there is a need for continuous improvement and more effective preparation methods.